Medical devices developed for implantation or insertion into patients are known for various purposes including stenting, drainage, etc., of lumens, tracts, vessels, and cavities within the body. As an example, polymeric ureteral stents are widely used to facilitate drainage in the upper urinary tract (e.g., drainage from the kidney to the bladder), for example, following ureteroscopy, endourerotomies, and endopyelotomy for ureteral strictures, as well as in other instances where ureteral obstruction may occur.
An exemplary stent 10 of this type is illustrated in FIG. 1. The stent 10 has a proximal end 10p and a distal end 10d. It is a tubular polymer extrusion having a shaft 12, a distal renal retention structure (e.g., renal “pigtail” 14), and a proximal retention structure (e.g., bladder “pigtail” 16). These retention structures prevent upward migration of the stent toward the kidney or downward migration of the stent toward the bladder. Once properly deployed in the ureter, the stent 10 provides ureteral support and allows the passage of urine. The stent 10, as exemplified by FIG. 1, may further be provided with any one or more of the following: (a) a tapered tip 11, to aid insertion, (b) multiple side ports 18 (one numbered), which are typically arranged in a spiral pattern down the length of the body to promote drainage, (c) graduation marks 25 (one illustrated), which are normally used for visualization by the physician to know when the appropriate length of stent has been inserted into the ureter, and (d) a suture 22, which aids in positioning and withdrawal of the stent.
During placement, such ureteral stents 10 are typically placed over a urology guide wire, through an access sheath, and advanced into position with a pusher. Once the distal end of the stent is advanced into the kidney/renal calyx, the guide wire is removed, allowing the pigtails 14, 16 to form in the kidney 19 and bladder 20, as shown in FIG. 2. The renal pigtail 14 of the stent may be closed or tapered on the end, depending on the method of insertion (e.g., the use of a guide wire or otherwise). As shown in FIG. 2, the stent 10 extends through the ureteral orifice 21a and into the bladder 20. The other ureter entering bladder 20 through the opposite ureteral orifice 21b is not shown.
These types of implanted medical devices may be associated with patient discomfort or pain after being positioned within the body, for example, in regard to ureteral stents, pain and/or discomfort in the bladder and flank area after insertion. Another potential issue is that various applications and anatomies require medical devices of different diameters and lengths, e.g., differences in individual ureteral anatomies require different diameters and lengths between the end retention structures of ureteral stents. Consequently, hospitals and other facilities inventory stents of different diameters and for each diameter, stents of different lengths, in some cases as much as six stents of different lengths for each diameter.
Generally, a physician must estimate ureter length before beginning a procedure. If the estimate is near the end of a particular length range of stents that are kept on hand, it is possible to select a stent that is slightly too long or too short. However, that fact may not be ascertainable until the stent has been implanted. The procedure for correcting any incorrect selection involves removing that stent and placing a longer or shorter stent in the ureter thereby complicating the procedure and potentially increasing patient trauma.
Variable length stents include offset, planar, or nautilus coils at one or both of the end retention structures that can be unwound to increase or decrease the effective length between the structures. Another ureteral stent example includes a stent with multi-turn coils at the bladder end that may be clipped off outside of the body when the length of the stent has been estimated by the physician.
Although these examples may reduce inventory requirements, excess retention structure left in the bladder may occupy a considerable volume which may increase a risk of tissue irritation. Additionally, stents clipped to length outside of the body prior to placement may ultimately result in a length that is too short, requiring a new stent to be used, or too long, in which case the excess material and irritation concerns remain. Therefore, there exists a need for medical devices and methods to trim a stent within the patient to ensure that it is sized accurately and consistently without excess volume leftover that may cause irritation.